A 30-year-old university drop-out posed as a doctor and sexually abused a 16-year-old boy.
A Leicestershire court heard that Dean Matthews - who had previously masqueraded as a heart surgeon - befriended the teenager's father in a cafe and claimed to be a GP.
He overheard the man - who suffered from heart disease and diabetes - complaining about the care he was getting from his GP.
Matthews introduced himself as Dr Andrew McCormack and offered to help him. He claimed he was based at a city medical centre, but was on leave and lecturing.
He later met the man again in the same cafe, and after giving him medical advice, telephoned a health centre and helped him to sign up there as a patient.
The court heard that a 'trust was developing' between the two men, and the father eventually told 'Dr McCormack' about his son, and a medical condition he had.
It led to Matthews offering to examine the youth at the family's home on December 7 last year. When left alone with the teenager, he carried out an unnecessary intimate examination.
The police were eventually called when the father discovered no GPs at the medical centre went by the name of Dr McCormack.
The 30-year-old admitted sexually assaulting the boy, and twice supplying the dad with the prescription-only drug diazepam.
The prosecution said the assault on the teenager had 'a devastating effect' on his family.
The court was told that Matthews was a former bio-medical sciences student at De Montfort University.
In 2008, he was was caught dressed as a surgeon and impersonating a heart specialist by staff at Leicester Royal Infirmary. His university was informed, but no prosecution resulted, although he was banned from attending the hospital for his course. He was also referred to a psychiatrist, and later dropped out of his degree course.
Carl Gaskell, mitigating, said his client 'genuinely believed he was a doctor' because of his mental health issues at the time. He said he was 'no longer under that misconception'.
Sentencing Matthews to 12 months, Judge Simon Hammond said: "I can't accept he genuinely believed he was a doctor. It must be a nonsense."